The present invention relates generally to a scum removal system for removing floating materials such as oil, scum, floating bodies and the like from the surface of a sewage settling tank.
In scum removal systems of the prior art, apparatus such as a wiper of one sort or another is moved across the surface of the liquid to push the floating materials toward a scum trough located at one end of the settling tank. The upper edge of the trough is located above the level of the liquid in the tank and a structure known in the art as a beach is inclined downward from the top of the trough into the liquid. With this arrangement, the wiper scrapes the floating material up the inclined beach and over into the trough. For example, British patent specification No. 390,989 illustrates a skimmer which is mounted to a floating body and a typical inclined beach.
According to the invention, the skimmer itself floats on the liquid in the settling tank and is urged along by a floating carriage. Further, the upper edge of the scum trough is below the average level of liquid in the tank. A floating beach fixed to the upper edge of the trough rises above the liquid level to prevent liquid from flowing over into the trough. As the skimmer approaches, the beach is submerged to permit flow over the beach and into the trough. This flow carries with it the floatable materials which have been collected by the skimmer. Flow over the beach is controlled by depth to which the beach is submerged and the length of time the beach remains submerged. The skimmer itself is stopped short of contact with the beach and is lifted from the surface of the liquid for movement back to the opposite end of the tank where the skimmer is again lowered onto the liquid. Both the lifting and lowering of the skimmer is accomplished by a system of inclined ramps, stops and nests.